The invention relates to a device for monitoring the operation of lamps, particularly headlamps and tail lamps in automotive vehicles and the like, and in particular to a device of the type which applies a signal to an indicator in the event that one of the lamps being monitored becomes inoperative.
It is known to monitor the operation of pairwise arranged vehicle lamps by means of a differential relay. In such case, the relay is comprised of two windings having the same number of turns. One winding is connected in the current path of one of the lamps, and the other winding is connected in the current path of the other of the lamps. The windings are so wound and/or so connected in the current path of the respective lamps that when current flows through both the windings the magnetic field produced by the current in one winding at least partly cancels out the magnetic field produced by the current in the other winding. If one of the two lamps becomes operative, for example burns out, so that lamp current no longer flows through the current path of such lamp, then the magnetic field associated with such lamp ceases to exist, and the remaining magnetic field activates the armature of the relay thereby effecting closing of a switch which applies a signal to an indicator arrangement. Each such pair of lamps must have associated with it such a differential relay and an indicator arrangement. If only one indicator arrangement is to be used, an additional relay is required for coupling the circuit, so that considerable expense for a space-consuming arrangement is required.